Saturday, November 19, 2016

Radiotelephones came into use in the 1920's and 1930's.  Radiotelephones are a means of voice communications with a shore or ship telephone via marine operator, directly with a dispatcher, agent or owner, or directly with other vessels. The first radiotelephones were amplitude modulated (AM).  These were subject to interference by atmospheric noise and man-made noise.  The operating frequencies range between 2 and 23 Megahertz; the operating range under favorable conditions is several thousand miles. In the 1950's a very high frequency (VHF) band of frequencies was set aside for marine use.  At first there were 26 channels.  Communication is essentially line-of-sight, making the useful range about 20 miles offshore from a shore station.  In the late 1960's the number of channels was doubled by making each channel half of the bandwidth (50 kilohertz per channel was changed to 25 kilohertz). The VHF marine channels are frequency modulated (FM), providing some immunity to noise. In the 1960's, Single Sideband (SSB) began to come into use.  SSB has an advantage of needing less than one-half the bandwidth that AM requires.  With the reduced bandwidth, interference by noise is somewhat reduced, and the number of available channels was more than doubled.  The use of SSB was encouraged.  In 1977 AM usage by law ceased; all high seas communications were mandated to be SSB.

VHF-Radio Telephone
Modar Electronics – D33ADA1020A

Manufactured by: Modar Electronics, Subsidiary of Motorola
Model: D33ADA1020A
Capacity: 55 Channels Synthesized, 25W/1W
Frequency Range: 156-157.45 MHz TX, 156-163 MHz RX
Power Requirement: 12VDC


Standard Comm. Corp. – Horizon MAXI

Manufactured by: Standard Comm. Corp.
Model: Horizon MAXI
Capacity: 55 Channels Synthesized, 25W/1W
Frequency Range: 156-157.45 MHz TX, 156-163 MHz RX

Intech – V-108

Manufactured by: Intech
Model: V-108
Date of Mfg: 1-78
Capacity: 12 Channels, Crystal, 25W/1W
Power Requirement: 12VDC 5 Amp


Cybernet – CTX7800S

Manufactured by: Cybernet
Model: CTX7800S
Capacity: 55 Channels, Synthesized, 25W/1W


Intech – Mariner 90

Manufactured by: Intech
Model: Mariner 90
Date of Mfg: 4-81
Capacity: 55 Channels, Synthesized, 25W/1W

Konigsberg Electronics – KR-25W

Manufactured by: Konigsberg Electronics (Konel)
Model: KR-25W
Capacity: 12 Channels, Crystalled, 25W/1W

Ray Jefferson – 7878M

Manufactured by: Ray Jefferson, Div of Jetronic Industries Inc.
Model: 7878M
Capacity: 55 Channels, Synthesized, 25W/1W

Single Sideband Receivers
Harris – RF-230M

Manufactured by: Harris
Model: RF-230M
Capacity: 95 Channels Synthesized
Frequency Range: 2-23MHz 

Hull – 922

Manufactured by: Hull
Model: 922
Capacity: 22 Channels Synthesized
Frequency Range: 2-10MHz

Northern Radio Company – N550A

Manufactured by: Northern Radio Company
Model: N550A
Capacity: 48 Channels Synthesized
Frequency Range: 2-23MHz

Intech – Mariner 500

Manufactured by: Intech
Model: Mariner 500
Date of Mfg: 9-83
Capacity: 12 Channels
Frequency Range: 2-3.4MHz

Power Requirement: 13.6VDC 20 Amp

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